The difference between Modbus TCP and Modbus RTU protocol

The difference between Modbus TCP and Modbus RTU protocol

　　 The Modbus protocol includes ASCII, RTU, TCP, etc., and does not specify the physical layer. This protocol defines the message structure that the controller can recognize and use, regardless of what kind of network they communicate through. The standard Modicon controller uses RS232C to implement serial Modbus. Modbus's ASCII and RTU protocols stipulate the structure of messages, data, commands, and answering methods. The data communication adopts the Maser/Slave mode. The Master sends a data request message, and the Slave can send the data to the Master after receiving the correct message. In response to the request; the Master can also directly send messages to modify the data on the Slave to achieve two-way reading and writing.

　　 Modbus has the following characteristics:

　　(1) Standard and open, users can use Modbus protocol for free and with confidence, without paying license fees, and will not infringe on intellectual property rights. Currently, there are more than 400 manufacturers supporting Modbus and more than 600 products supporting Modbus.

　　 (2) Modbus can support a variety of electrical interfaces, such as RS-232, RS-485, etc., and can also be transmitted on various media, such as twisted pair, optical fiber, wireless, etc.

　　(3) Modbus frame format is simple, compact and easy to understand. It is easy for users to use and easy for manufacturers to develop.

　　Modbus rtu and Modbus tcp are both MODBUS protocols in essence, both rely on MODBUS register addresses to exchange data; but the hardware interfaces used are different. Modbus RTU generally uses serial port RS232C or RS485/422, while Modbus TCP generally uses Ethernet Network port. There are many protocol converters on the market now, which can easily convert these different protocols to each other.

　　 In fact, the Modbus protocol includes ASCII, RTU, and TCP.

　　The standard Modicon controller uses RS232C to realize serial Modbus. Modbus's ASCII and RTU protocols stipulate the structure of messages and data, the way of command and answer, and the data communication adopts the Maser/Slave way.

　　 The Modbus protocol needs to check the data. In addition to the parity check in the serial protocol, the ASCII mode uses the LRC check, and the RTU mode uses the 16-bit CRC check.

　　 ModbusTCP mode does not require additional verification, because the TCP protocol is a connection-oriented reliable protocol.

　　 TCP and RTU protocols are very similar, just remove the two-byte check code of the RTU protocol, and then add 5 0 and a 6 at the beginning of the RTU protocol and send it out through the TCP/IP network protocol.